Posts Tagged ‘map projections’

[Editor’s note: No PRJ file? No problem. Use this new guide by M. Maher from ESRI Press to learn map projection basics and the ArcGIS commands (versions 9 and 10) that register map data to common coordinate spaces. Read the first chapter and table of contents at ESRI.]

‘Lining Up Data in ArcGIS‘ – a guide to map projections is a new book from ESRI Press. It is authored by Margaret M. Maher. Since I don’t have ArcGIS running in my office I couldn’t try out some of the details provided in the book, nevertheless, I did spend some time running through the book and offer the following comments.

One of the issues that many people encounter with GIS data revolves around projections, coordinates and lining up data with already existing spatial information. I’ve made the mistake myself numerous times, excited to get the data into the system, only to open the map window and finding what I just added from Berlin is placed in Oklahoma, Alberta or the middle of the Mediterranean Sea. How did that happen? Because I never lined up the data properly.

This book is very helpful. It explains how to identify geographic coordinate systems as compared to projected coordinate systems. If you are using ArcMap, then this book will show exactly how to determinine projections and set them. It even provides examples for going to ArcGIS Online, downloading imagery and aligning it properly.

[Editor’s note: Best practices on accounting for area-distortions normally present in conformal map projections by using cartograms and value-by-alpha alternatives. Check out the paper. Thanks ChartPorn!]

The latest issue of the The Cartographic Journal (of the British Cartographic Society) contains a paper written by Robert Roth, me, and Zachary Johnson entitled “Value-by-alpha Maps: An Alternative Technique to the Cartogram.” The value-by-alpha map is something I have touched on here several times over the past year and a half (as has Zach on his blog), and about which I spoke at last year’s NACIS conference in Sacramento. With the publication of this paper, it’s high time I explained what it’s all about.

Value-by-alpha maps (hereafter shortened to VBA), like everything noble and good, have their roots in somebody complaining about something on the internet—me, about election cartograms. Seeking an alternative to what I think are ugly and unreadable election results cartograms, I worked with my Axis Maps dudes to create a 2008 U.S. election map that used transparency rather than size to vary the visual impact of map units, thinking that avoiding the distortion of these units into unrecognizable sizes and shapes would make the map easier to read.

Rob Roth, a stellar Ph.D. candidate and shameless county collector at Penn State (studying under The Beard himself, the illustrious Alan MacEachren) became interested in further developing the idea academically and enlisted my Axis Maps partner and radical raw milk zealot Zach Johnson (who wrote his master’s thesis on cartograms) and I to collaborate on the now-published Cartographic Journal article. We were all graduate students at Madison together once upon a time, and we make a good team—striking a perfect balance between study, practice, and chili-eating.

Enough backstory. I’ll summarize at moderate length the idea and what we wrote.